P1794

P1794-SPEED SENSOR GROUND ERROR





For a complete wiring diagram Consult Diagrams/Electrical.

Theory of Operation

The input and output speed sensors use a common ground circuit. The loss of this common ground results in the input signal being sensed for both. After a reset in neutral, and after observing a specific ratio, a Speed Check Fault Counter will increment. Because the speed sensors and the thermistor share the same ground circuit, this DTC may indicate a loss of the common ground. In some cases this fault will cause a Gear Ratio Error DTC to be set.

- When Monitored:
Every 7ms after a controller reset with transmission in neutral.

- Set Condition:
After a PCM reset in neutral and the input to output sensor ratios equal 2.50 to 1.0 ± 50.0 rpm.





Always perform the 40/41TE Pre-Diagnostic Troubleshooting procedure before proceeding. Testing and Inspection

Diagnostic Test

1. PCM AND WIRING
Turn the ignition off to the lock position.
Remove the Ignition Switch Feed fuse from the TIPM.

CAUTION: Removal of the Ignition Switch Feed fuse from the TIPM will prevent the vehicle from being started in gear.

WARNING: The Ignition Switch Feed fuse must be removed from the TIPM. Failure to do so can result in personal injury or death.

Install the Transmission Simulator, Miller tool #8333 and the Electronic Transmission Adapter kit.
Ignition on, engine not running.
With the Transmission Simulator, set the "Input/Output Speed" switch to "ON" and the rotary switch to the "3000/1250" position.
With the scan tool, monitor the Input and Output Speed Sensor readings.
Does the Input to Output speed read 3000/1250 rpm (± 50 rpm)?

Yes

- Go To 3

No

- Go To 2

2. (T13) SPEED SENSOR GROUND CIRCUIT OPEN








Turn the ignition off to the lock position.
Disconnect the PCM C4 harness connector.
Disconnect the Input and Output Speed Sensor harness connectors.

NOTE: Check connectors - Clean/repair as necessary.

CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.

Measure the resistance of the Input and Output (T13) Speed Sensor Ground circuits between the Input and Output Speed Sensor harness connectors and the appropriate terminal of Miller tool #8815.
Is the resistance above 5.0 ohms on either circuit?

Yes

- Repair the (T13) Speed Sensor Ground circuit for an open.
- Perform 40/41TE VERIFICATION TEST Transmission Verification Test

No

- Using the schematics as a guide, check the Powertrain Control Module (PCM) terminals for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. Check for any Service Information Tune-ups or Service Bulletins for any possible causes that may apply. If no problems are found, replace and program the PCM. With the scan tool, perform Quick Learn.
- Perform 40/41TE VERIFICATION TEST Transmission Verification Test

3. INTERMITTENT WIRING AND CONNECTORS
The conditions necessary to set the DTC are not present at this time.
Using the schematics as a guide, inspect the wiring and connectors specific to this circuit.
Wiggle the wires while checking for shorted and open circuits.
With the scan tool, check the DTC EVENT DATA to help identify the conditions in which the DTC was set.
Were there any problems found?

Yes

- Repair as necessary.
- Perform 40/41TE VERIFICATION TEST Transmission Verification Test

No

- Test Complete.